B.12 User-Controllable Variables

AOInts has been optimally constructed so that the fastest integral algorithm for ERI calculation is chosen for the given integral class and batch. Thus, the user has not been provided with the necessary variables for overriding the program’s selection process. The user is, however, able to control the accuracy of the cutoff used during shell-pair formation (METECO) and the integral threshold (THRESH). In addition, the user can force the use of the direct SCF algorithm (DIRECT_SCF) and increase the default size of the integrals storage buffer (INCORE_INTS_BUFFER).

Currently, some of Q-Chem’s linear scaling algorithms, such as QCTC and ONX algorithms, require the user to specify their use. It is anticipated that further research developments will lead to the identification of situations in which these, or combinations of these and other algorithms, will be selected automatically by Q-Chem in much the same way that PRISM algorithms choose the most efficient pathway for given integral classes.